To maintain a proper fuel-air mixture to an IC engine, the quantity of fuel being supplied should be made dependent, among others, on the temperature of the air being supplied to the engine. To sense the temperature, a temperature sensor is needed which is sturdy and suitable for operation in the rough environmental conditions of automative engines, and which additionally can rapidly follow changes in temperature. The temperature sensor thus must have only a low heat capacity. The thermal coupling of the temperature sensing element itself with the holder or housing must be so designed that the response speed of the sensor is unaffected by the housing or holder. Additionally, the air which is to be sensed should be supplied to the sensor in such a way that the air flow characteristic are an optimum to provide optimum sensing of the temperature. The sensing element, typically, is a sensing resistor which should be surrounded by the air flow. The sensing resistor or sensing element must, additionally, be protected from contamination, damage, or even destruction by outside mechanical influences. The measuring resistor and its contact elements must be protected against corrosion due to ambient humidity and contaminants in the air passing the sensor which, for example, may include remnants of salt spray after winter-salting of roads or the like. A sensor of this type is described and claimed in U.S. Pat. No. 4,368,453, HERDEN et al., assigned to the assignee of this application.
It is difficult to meet all these requirements since, if the measuring resistor is to have a protective coating, it should be as thin as possible so as not to interfere with high response speed, but still be of sufficient strength and thickness to properly protect the sensor. Very thin coatings on resistance elements are insufficient to properly protect the sensor, and particularly at the solder terminals, namely at the transition between the resistance layer and the solder connections, and do not form the hermetical covering over the entire sensing unit.